The 15-acre relic at the foot of Houston Street, where Holland America liners once set sail across the Atlantic, now threatens to sink the finances of the Hudson River Park of which it’s part.

Under state law, the pier is supposed to generate revenue to help pay for upkeep of the five-mile waterfront park. But Madelyn Wils, CEO of the Hudson River Park Trust — the city-state partnership that operates it — says the pier is now making only $5 million a year while costing $7 million to maintain.

It’s deteriorated so badly, some estimate it might have to close by 2014 without big bucks to repair it.

Sprawling Pier 40 might be the most underutilized indoor-outdoor structure in Manhattan, eerily deserted on a bright summer afternoon. Few venture out to its western-most end despite eye-popping views.

Other than a bizarrely shaped, three-level parking garage around a ballfield, it’s home only to the Trust’s offices, a few boating facilities and, on the windswept roof, the Trapeze School of New York.

The Post’s Annie Karni yesterday reported that Durst wants to create more revenue-producing space by shrinking the garage, and he opposes an idea that’s been floated to build apartments and a hotel on the pier.

Durst — chairman of nonprofit Friends of Hudson River Park, the Trust’s fundraising partner — shared more specifics with Realty Check. He and consultant Ben Korman, a Friends board member who once managed the pier, want to “consolidate” the garage into a “footprint” two-thirds smaller.

It would have the same number of parking spaces, currently 1,700, by converting it from a self-parking facility to one with attendants who would move cars into a three-level “stack,” which would fit into the existing ground floor with 20-foot ceilings.

Freeing up the second floor and roof would make room for 500,000 square feet of commercial space, Durst said. But he wouldn’t build or operate it himself; rather, the Trust would solicit proposals from other developers.

At the same time, Durst laughed off what he called a “flawed” study commissioned by the Trust that floated the idea that Pier 40 could be used for apartment towers and a hotel, which could generate $9 million to $20 million a year. (Wils said she didn’t necessarily back the apartments plan but was interested in exploring options.)

Durst, stating he was speaking not as Friends chairman but as “a private individual with knowledge of residential development,” said, “I can unequivocally state that housing cannot help Pier 40 on a timely basis.”

That’s because any use of the pier other than for parking or retail requires Albany to rewrite a 14-year-old law governing uses of the Hudson River Park. It would also have to go through the city’s time-consuming Uniform Land Use Review Process.

Durst doesn’t believe his plan would take nearly as long. An outside firm operates the garage under a management contract but doesn’t have a lease, and so work could theoretically start right away.

But Wils said that creating new commercial space under Durst’s plan would still need state approval. However, Korman said that because it would be “less controversial” than apartment towers, it would need less time in Albany.